The invention relates to a security document containing a security means in which certain specific properties are detectable.
The equipment and techniques at the disposal of forgers are evolving and now enable them to copy quickly and more readily duplicate the authentication means and techniques, particularly in the case of banknotes currently used, thus compelling a constant search for new security devices.
As a precaution against counterfeit security documents such as banknotes, bonds, stocks, identification cards, checks and other valuable documents, it has been proposed to use various security means such as watermarks, colored and/or metallic or metallized fibers, absence of optical bleach, or security strips or wires, whether these are printed, metallized, fluorescent or magnetic. Such security means are known as "recognition means" as they permit authentication of such documents. (See for reference, GB-A-1 363 244, GB-A-440 421 and EP-A-66 854).
The development of new security means has therefore been directed toward highly technical products with, for example, security means which, by their very nature, complexity or other factors, will not normally be available to forgers before at least a few years, and which are readily identifiable by the general public without the need to use sophisticated equipment. In addition, these products can be authenticated by professional users such as banks by way of reliable and instantaneous automatic control means.
Utilization by the general public normally leads to the use of optical systems permitting visual identification under natural or artificial lighting, such as obtained with a WOOD lamp.
It is, for example, already known to use synthetic fibers containing luminescent substances based on rare earth metals in their mass or on their surface. (See for reference EP-A-66854 and FR-A-1 522 465.) However, such means can prove unreliable when they are destined for use by the general public, since they can be forged by printing with ink or varnish containing similar substances. (See for reference FR-A-1471367).
Other security documents, such as those in GB-A-2 148 486, GB-A-2099756, U.S. Pat. Nos. 4,138,057 and 3,728,521, comprise a base material incorporating at least one optical fiber, and generally an assembly of several optical fibers intended to form coded information. Authentication of the document is achieved by illuminating one end of the fibers and observing the light transmitted to the other end. Such a technique requires relatively complicated detection means in order to allow for adequate illumination and observation of the ends of the optical fibers. Moreover, these documents are fragile, and any incidental or unintentional breakage of one fiber will prevent transmission of light and thus distort the observed message.